This invention pertains to an improved apparatus and method of producing viscous oil from a subsurface formation. More particularly, electrical formation heating and one or more slanted or horizontal boreholes extending from the same production well are combined to enhance the amount of oil produced with a given amount of electrical power.
For many years, it has been known that large deposits of relatively shallow, viscous oil are present in subterranean formations. Normally, the viscous oil is produced through a vertical production well. The well productivity is nearly inversely proportional to the viscosity of the oil. It has been proposed, for example, in U.S. Pat. Nos. 3,642,066; 3,874,450; 3,848,671; 3,948,319; 3,958,636; 4,010,799 and 4,084,637, to use electrical current to add heat to a subsurface pay zone containing tar sands or viscous oil to render the viscous hydrocarbon more flowable. Electrodes are connected to an electrical power source and are positioned at spaced apart points in contact with the earth. Currents up to 1200 amperes are passed between the electrodes. This heats oil in the formation. Electrical power utilizes energy from various sources. This energy is expended for viscous oil. Therefore, the relative success of electric heating is dependent on the amount of oil produced per unit of electric power applied. The effectiveness of the electrical process is partially limited by the effective radius of the borehole, for example, a radius of 0.5 foot, into which the oil flows from the formation.
In normal oil and gas producing operations, for various reasons, for example intersecting thin strata, it has been proposed to drill a slanted or essentially horizontal well. At an appropriate point in the earth, an essentially vertical borehole is deviated or drilled through an appropriate radius of curvature so as to extend laterally away from the vertical axis of the vertical borehole and extend either in a slanted manner or in an essentially horizontal manner through a portion of the formation.
It is the primary objective of this invention to increase oil production from a subsurface viscous oil bearing formation by combining electrical heating with one or more laterally extending slanted or horizontal boreholes having an effective production radius greater than normal.